(PureBasic) Validate a JWS Using ECDSA P-256 SHA-256

Validates a JSON Web Signature (JWS) that uses ECDSA P-256 SHA-256

Note: This example requires Chilkat v9.5.0.66 or greater.

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IncludeFile "CkJws.pb"
IncludeFile "CkStringBuilder.pb"
IncludeFile "CkJsonObject.pb"
IncludeFile "CkPublicKey.pb"

Procedure ChilkatExample()

    ; This requires the Chilkat API to have been previously unlocked.
    ; See Global Unlock Sample for sample code.

    ; Note: This example requires Chilkat v9.5.0.66 or greater.

    ; This example takes a JSON signature in compact serialization format,
    ; and uses an ECDSA public key to validate and recover the protected header and payload.

    ; We only need a public key for signature validation.  This is the ECDSA public key
    ; that is used:

    ;      {"kty":"EC", 
    ;       "crv":"P-256", 
    ;       "x":"f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU", 
    ;       "y":"x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0" 
    ;      } 

    sbPubKey.i = CkStringBuilder::ckCreate()
    If sbPubKey.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkStringBuilder::ckAppend(sbPubKey,"{" + Chr(34) + "kty" + Chr(34) + ":" + Chr(34) + "EC" + Chr(34) + ",")
    CkStringBuilder::ckAppend(sbPubKey,Chr(34) + "crv" + Chr(34) + ":" + Chr(34) + "P-256" + Chr(34) + ",")
    CkStringBuilder::ckAppend(sbPubKey,Chr(34) + "x" + Chr(34) + ":" + Chr(34) + "f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU" + Chr(34) + ",")
    CkStringBuilder::ckAppend(sbPubKey,Chr(34) + "y" + Chr(34) + ":" + Chr(34) + "x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0" + Chr(34))
    CkStringBuilder::ckAppend(sbPubKey,"}")

    pubKey.i = CkPublicKey::ckCreate()
    If pubKey.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success.i = CkPublicKey::ckLoadFromString(pubKey,CkStringBuilder::ckGetAsString(sbPubKey))
    If success <> 1
        Debug CkPublicKey::ckLastErrorText(pubKey)
        CkStringBuilder::ckDispose(sbPubKey)
        CkPublicKey::ckDispose(pubKey)
        ProcedureReturn
    EndIf

    jws.i = CkJws::ckCreate()
    If jws.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; Set the ECC public key:
    signatureIndex.i = 0
    CkJws::ckSetPublicKey(jws,signatureIndex,pubKey)

    ; Load the JWS.
    sbJws.i = CkStringBuilder::ckCreate()
    If sbJws.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkStringBuilder::ckAppend(sbJws,"eyJhbGciOiJFUzI1NiJ9")
    CkStringBuilder::ckAppend(sbJws,".")
    CkStringBuilder::ckAppend(sbJws,"eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt")
    CkStringBuilder::ckAppend(sbJws,"cGxlLmNvbS9pc19yb290Ijp0cnVlfQ")
    CkStringBuilder::ckAppend(sbJws,".")
    CkStringBuilder::ckAppend(sbJws,"DtEhU3ljbEg8L38VWAfUAqOyKAM6-Xx-F4GawxaepmXFCgfTjDxw5djxLa8ISlSA")
    CkStringBuilder::ckAppend(sbJws,"pmWQxfKTUJqPP3-Kg6NU1Q")

    success = CkJws::ckLoadJwsSb(jws,sbJws)
    If success <> 1
        Debug CkJws::ckLastErrorText(jws)
        CkStringBuilder::ckDispose(sbPubKey)
        CkPublicKey::ckDispose(pubKey)
        CkJws::ckDispose(jws)
        CkStringBuilder::ckDispose(sbJws)
        ProcedureReturn
    EndIf

    ; Validate the 1st (and only) signature at index 0..
    v.i = CkJws::ckValidate(jws,signatureIndex)
    If v < 0
        ; Perhaps Chilkat was not unlocked or the trial expired..
        Debug "Method call failed for some other reason."
        Debug CkJws::ckLastErrorText(jws)
        CkStringBuilder::ckDispose(sbPubKey)
        CkPublicKey::ckDispose(pubKey)
        CkJws::ckDispose(jws)
        CkStringBuilder::ckDispose(sbJws)
        ProcedureReturn
    EndIf

    If v = 0
        Debug "Invalid signature.  The ECC key was incorrect, the JWS was invalid, or both."
        CkStringBuilder::ckDispose(sbPubKey)
        CkPublicKey::ckDispose(pubKey)
        CkJws::ckDispose(jws)
        CkStringBuilder::ckDispose(sbJws)
        ProcedureReturn
    EndIf

    ; If we get here, the signature was validated..
    Debug "Signature validated."
    Debug "--"

    ; Recover the original content:
    Debug "Recovered content:"
    Debug CkJws::ckGetPayload(jws,"utf-8")
    Debug "--"

    ; Examine the protected header:
    joseHeader.i = CkJws::ckGetProtectedHeader(jws,signatureIndex)
    If CkJws::ckLastMethodSuccess(jws) <> 1
        Debug "No protected header found at the given index."
        CkStringBuilder::ckDispose(sbPubKey)
        CkPublicKey::ckDispose(pubKey)
        CkJws::ckDispose(jws)
        CkStringBuilder::ckDispose(sbJws)
        ProcedureReturn
    EndIf

    CkJsonObject::setCkEmitCompact(joseHeader, 0)

    Debug "Protected (JOSE) header:"
    Debug CkJsonObject::ckEmit(joseHeader)
    CkJsonObject::ckDispose(joseHeader)

    ; Output:

    ; 	Signature validated.
    ; 	--
    ; 	Recovered content:
    ; 	{"iss":"joe",
    ; 	 "exp":1300819380,
    ; 	 "http://example.com/is_root":true}
    ; 	--
    ; 	Protected (JOSE) header:
    ; 	{ 
    ; 	  "alg": "ES256"
    ; 	}


    CkStringBuilder::ckDispose(sbPubKey)
    CkPublicKey::ckDispose(pubKey)
    CkJws::ckDispose(jws)
    CkStringBuilder::ckDispose(sbJws)


    ProcedureReturn
EndProcedure